1. Field of the Invention
The present invention relates to an abnormality diagnosis device of an internal combustion engine provided with multiple injectors for each cylinder of the internal combustion engine.
2. Description of Related Art
As described in Patent document 1 (JP-A-2006-299945), there is a system that is provided with two injectors in two intake ports of each cylinder of an internal combustion engine respectively and that injects fuel into each cylinder through the two injectors, aiming at atomization of a fuel spray and formation of a suitable mixture gas inside the cylinder, for example.
As described in Patent document 2 (JP-A-H8-338285), there is another system that determines an air-fuel ratio of each cylinder based on an output of an air-fuel ratio sensor provided at an exhaust gas merging section, at which exhaust gas of the respective cylinders of the internal combustion engine gathers and flows, and that controls the air-fuel ratio (or fuel injection quantity) for each cylinder.
For example, when the injector of a certain cylinder breaks down and the air-fuel ratio (or the fuel injection quantity) of the cylinder changes, the cylinder causing the abnormal air-fuel ratio can be specified by determining the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor with the use of the technology of above-described Patent document 2.
In the system that is provided with the two injectors for each cylinder of the internal combustion engine as in the technology of above-described Patent document 1 for example, when one of the two injectors provided to a certain cylinder breaks down and the air-fuel ratio (or the fuel injection quantity) of the cylinder changes, the cylinder causing the abnormal air-fuel ratio can be specified by using the technology of above-described Patent document 2. However, it cannot be determined which one of the two injectors of the abnormal cylinder is abnormal. Therefore, replacement of both of the two injectors of the abnormal cylinder at a service shop or the like is necessary. Accordingly, the replacement work is time consuming and a cost of replacement parts is high.
As described in Patent document 3 (JP-A-S63-94057), there is another system that is provided with two injectors in two intake ports of each cylinder of the internal combustion engine respectively and that injects fuel through the two injectors for each cylinder, aiming at atomization of a fuel spray or reduction of port wetting (i.e., reduction of adhesion of the fuel to an intake port inner wall) in each cylinder of the internal combustion engine, for example.
As described in Patent document 4 (JP-A-2007-85176), there is yet another system that determines existence or nonexistence of abnormality in an air-fuel ratio of each cylinder (i.e., an abnormality of an injector) based on an output of an air-fuel ratio sensor provided at an exhaust gas merging section, at which exhaust gas of the respective cylinders of an internal combustion engine gathers and flows.
In the case where the abnormality diagnosis technology of Patent document 4 is applied to the internal combustion engine of Patent document 3 provided with the two injectors for each cylinder, if either one of the two injectors of a certain cylinder causes an abnormality, the cylinder causing the abnormal air-fuel ratio due to the abnormality in the injector can be specified. However, it is impossible to specify which one of the two injectors of the abnormal cylinder is abnormal. Therefore, replacement of both of the two injectors of the abnormal cylinder at a service shop or the like is necessary. Accordingly, the replacement work is time consuming and a cost of replacement parts is high.